Track and vibrate: Tiny photosensors are embedded in the black fabric shown above. Blue vibrators also surround the subject’s wrist (left). The photosensors capture light emitted from nearby projectors to determine the position of the subject’s arm. Software then compares the real arm position (red line) with the ideal arm position (yellow line). The circles correspond to the vibrators; the green one will vibrate to indicate the correct position to the subject.
Because each Second Skin sensor has a unique ID, Raskar says that this will be more accurate than traditional optical systems, in which the reflectors worn by the subject are indistinguishable from each other and can cause errors when one reflector crosses another. What’s more, Raskar has shown that the system works outside and in the dark.
“In theory, everything his system can do, we could do by computer vision, but in practice we haven’t found a solution yet,” says Bregler. “With his sensors, it’s very accurate and very clear where [the person] is from frame to frame.”
For the movie industry, this potentially means that motion tracking can be done on a regular set, which would save production time and let the actors work in a natural setting. “These elaborate systems get in the way of trying to shoot these films,” says Steve Sullivan, the senior technology officer at Lucasfilm’s Industrial Light & Magic (ILM). “A lot of people see motion tracking as being a solved problem, but I think there’s much more we can do to make it more accessible to a range of people and less in the way.” ILM recently developed a special proprietary system of high-contrast bands for the on-set motion tracking for Pirates of the Caribbean 2 and Ironman, but the actors have to wear a special suit, and extensive post-processing is required, says Sullivan. “It’s great to hear that researchers are trying to tackle this problem, because it’s such an issue to have to break up production and shoot scenes and actors separately on these stages.”
“I think a lot of the potential for these kinds of low-end tracking technology is … more for new applications, where you can’t spend all the time to make it perfect,” says Michael Gleicher, an associate professor of computer science at the University of Wisconsin-Madison. Gleicher says that motion tracking is becoming more popular in video games that can track a player and react in real time.
The researchers have also shown that the system can be used to help track and correct motions in a simple tai chi exercise. Such a system incorporates tiny vibrators that move when the current position of the subject’s limb is off course to indicate to the subject the need for self-correction. In much the same way, the researchers speculate that the system could also be used for physical therapy or to track a subject’s movements, in order to prevent falls.
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